The Obama Administration wants to play tough with the Russian government over its invasion of Crimea by imposing sanctions targeting the assets of key Russian officials. But Russia has struck back by squeezing the place where it has great leverage over the United States—the space program.

Following his earlier suggestion that NASA astronauts use a trampoline to reach the International Space Station, Russian Deputy Prime Minister Dmitry Rogozin, one of the officials targeted by U.S. sanctions, upped the ante this week. He announced via his English-language Twitter feed that the Russian space agency has no plans to continue cooperating with NASA on the ISS after its current obligation expires in 2020. He also said Russia would stop shipments of its RD-180 rocket engines, and as we've noted before, the U.S. relies on these engines for military space launches.

Some of this may be simple posturing. For one thing, NASA is only in the beginning stages of trying to talk its international partners into extending the life of the space station to 2024. "The Russians, frankly, they're not getting as much scientific return out of the station," says Jeffrey Hoffman, former NASA astronaut and current MIT professor, "and whether this is something that they might have done anyway, or they're using this as a way of putting pressure on NASA, I don't really know."

Still, the new threats could pack a punch if Russia follows through. Russia could put pressure on both manned and unmanned American spaceflight.

On the manned spaceflight front, NASA is now completely reliant on Russia's Soyuz spacecraft and rockets to get its astronauts to the International Space Station. That's been the situation since the space shuttle fleet retired in 2011. Russia now flies American astronauts for a cost of about $62.7 million per seat through 2015. NASA announced last month that it had agreed to purchase six more Soyuz seats through 2016 at $70.7 million each.

If Russia refused to fly American astronauts, then there's not much the U.S. can do about it. NASA has been working according to Congressional mandate on a new vehicle, the Space Launch System, which is over budget and behind schedule. Although the new vehicle's first flight is set for 2017, it is not expected to actually carry crew until 2021—a year after the space station is currently scheduled to shut down. Commercial spaceflight providers such as SpaceX and Sierra Nevada may soon be able to fly humans into orbit, but they're not ready to do so yet. SpaceX is the closest, and it has delivered only cargo to the ISS.

Hoffman says he thinks it's unlikely that the Russians would renege on the existing agreements to fly U.S. astronauts. In the meantime, he says he hopes current events "will encourage Congress to fully fund NASA's commercial crew project."

On the unmanned front, United Launch Alliance (ULA), the near-monopoly created by Boeing and Lockheed Martin for launching satellites for the Pentagon, depends on the Russian-built RD-180 to power the first stage of its Atlas V satellite launcher.

"This has been a long-standing issue," Hoffman says. "When Lockheed started operating the Atlas V with the Russian engines, the original idea was that at first we would buy the Russian engines and then start making them in the United States, which sounds good in principle. It turns out that the Russians have some very specialized metallurgical technologies for making rocket engines. To be honest, they make really good engines and they can do some things that nobody here has quite figured out how to do."

SpaceX recently filed a lawsuit arguing it should be allowed to compete for delivery of some of the military launches, and in doing so took a few shots at ULA for its reliance on Russian hardware. "To not be given the opportunity to compete at all, especially in light of the Air Force's stated interest in competition and current dependence on Russia for national security launches, just doesn't make any sense," SpaceX says on its website.

"If Lockheed really can't get the engines for the Atlas V, it might be a shot in the arm for SpaceX," says Hoffman.